In the cushioning of hydraulic cylinders it is known to provide a cushioning member, such as a spear projecting axially from the head end of the piston or a sleeve projecting axially from the rod end of the piston and disposed around the piston rod, which, during the cushioned portion of the piston stroke, enters a cylinder head bore to define therewith a restricted passage of decreasing flow area through which fluid is displaced from the cylinder. A common form of cushioning member is a spear or sleeve having a frusto-conical exterior surface which forms a variable area annular orifice in which the inside diameter varies in lineal manner. Aside from the difficulty and expense of accurately grinding such frusto-conical surface on the cushioning member such variable area orifice does not produce uniform decrease in piston velocity. To achieve uniform decrease in piston velocity requires that the tapered surface be paraboloidal which would entail yet added expense in the manufacture of the cushioning member.
In other known forms of cushioning members such as those which are cylindrical with an axial groove of progressively increasing depth or those which are tubular with a series of axially spaced holes through the wall thereof which are progressively covered as the cushioning member enters the cylinder head bore, paraboloidal characteristics in the decrease of the restricted flow area cannot be achieved except by expensive and complex machining operations.
It is also known from U.S. Pat. No. 3,964,370, granted June 22, 1976 to provide a stepped cylindrical cushioning member which cooperates with a cylinder head bore to form an annular cushioning orifice which is of progressively decreasing cross-section area and increasing axial length to achieve substantially uniform decrease in piston velocity with substantially constant deceleration to smoothly cushion the piston movement without objectionable shock load.